Prenatal nicotine exposure (PNE) caused by maternal cigarette-smoking is linked to defects in auditory and visual sensory processing, behavior, memory, language, and generalized intelligence. Exposure to environmental tobacco smoke (ETS), in utero and early life is also related to neurocognitive deficits, behavioral disorders, and lower IQ measured in childhood and adolescence. The human brain undergoes massive growth, differentiation and maturation in utero and the first year of life, making it especially vulnerable to neurotoxic insult. Nicotine, a well-documented neural teratogen, crosses the placental and blood brain barriers to bind to nicotinic acetylcholine receptors, which are extensively involved in growth, connectivity and function of developing fetal and infant neural circuits. Thus PNE or ETS may have long term impact on neurochemical, neural circuitry, and behavioral development. Nicotine exposure from breast milk of smoking mothers or from breast milk of non-smoking mothers living with a smoker, may also contribute added nicotine exposure during early brain development. Quantification of infant nicotine levels from these multiple sources has been done in few studies, and fewer still have studied nicotine in association with very early brain and neurocognitive function. Methods: We propose to use auditory event-related potentials (ERP) in young infants with and without perinatal nicotine exposure, to study biological markers of neural aberration that may herald future neurocognitive deficits. We will examine sensory and higher order auditory cognitive processing in 3 groups of infants: 50 infants of mothers who smoke (PNE), 50 infants of non-smoking mothers living with a smoker (ETS), and 50 infants from smoke-free homes (CTL). We will measure biomarkers of nicotine exposure in maternal hair, urine and expired air, and in infant urine. We will use well- validated tools to estimate age-appropriate development focusing on items dependent upon auditory processing. A long term goal is to identify and refine a neurophenotype of nicotine's detrimental effects on the developing brain, in order to inform early interventions in this important at-risk population. We plan to use acquired findings to support an application for more detailed, longitudinal study.